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buildroot/toolchain/toolchain-common.in
Thomas Petazzoni 6856e417da toolchain: add BR2_TOOLCHAIN_HAS_{SYNC_x, ATOMIC} hidden booleans 
Currently, Buildroot provides one BR2_ARCH_HAS_ATOMICS boolean option
to indicate whether the architecture supports atomic operations or
not. However, the reality of atomic operations support is much more
complicated and requires more than one option to be expressed
properly.

There are in fact two types of atomic built-ins provided by gcc:

 (1) The __sync_*() family of functions, which have been in gcc for a
     long time (probably gcc 4.1). They are available in variants
     operating on 1-byte, 2-byte, 4-byte and 8-byte integers. Some
     architectures implement a number of variants, some do not
     implement any, some implement all of them.

     They are now considered "legacy" by the gcc developers but are
     nonetheless still being used by a significant number of userspace
     libraries and applications.

     https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html

 (2) The __atomic_*() family of functions, which have been introduced
     in gcc 4.7. They have been introduced in order to support C++11
     atomic operations. In gcc 4.8, they are available on all
     architectures, either built-in or in the libatomic library part
     of the gcc runtime (in which case the application needs to be
     linked with -latomic). In gcc 4.7, the __atomic_*() intrinsics
     are only supported on certain architectures, since libatomic did
     not exist at the time.

For (1), a single BR2_ARCH_HAS_ATOMICS is not sufficient, because
depending on the architecture, some variants may or may not be
available. Setting BR2_ARCH_HAS_ATOMICS to false as soon as one of the
variant is missing would cause a large number of packages to become
unavailable, even if they in fact use only more common variants
available on a large number of architectures. For this reason, we've
chosen to introduce four new Config.in options:

 - BR2_TOOLCHAIN_HAS_SYNC_1
 - BR2_TOOLCHAIN_HAS_SYNC_2
 - BR2_TOOLCHAIN_HAS_SYNC_3
 - BR2_TOOLCHAIN_HAS_SYNC_4

Which indicate whether the toolchain support 1-byte, 2-byte, 4-byte
and 8-byte __sync_*() built-ins respectively.

For (2), we introduce a BR2_TOOLCHAIN_HAS_ATOMIC, which indicates if
the __atomic_*() built-ins are available. Note that it is up to the
package to link with -latomic when gcc is >= 4.8. Since __atomic_*()
intrinsics for all sizes are supported starting

We conducted a fairly large analysis about various architectures
supported by Buildroot, as well as with a number of different
toolchains, to check which combinations support which variant. To do,
we linked the following program with various toolchains:

int main(void)
{
	uint8_t a;
	uint16_t b;
	uint32_t c;
	uint64_t d;

	__sync_fetch_and_add(&a, 3);
	__sync_fetch_and_add(&b, 3);
	__sync_fetch_and_add(&c, 3);
	__sync_fetch_and_add(&d, 3);

	__sync_val_compare_and_swap(&a, 1, 2);
	__sync_val_compare_and_swap(&b, 1, 2);
	__sync_val_compare_and_swap(&c, 1, 2);
	__sync_val_compare_and_swap(&d, 1, 2);

	__atomic_add_fetch(&a, 3, __ATOMIC_RELAXED);
	__atomic_add_fetch(&b, 3, __ATOMIC_RELAXED);
	__atomic_add_fetch(&c, 3, __ATOMIC_RELAXED);
	__atomic_add_fetch(&d, 3, __ATOMIC_RELAXED);

	__atomic_compare_exchange_n(&a, &a, 2, 1,  __ATOMIC_RELAXED,  __ATOMIC_RELAXED);
	__atomic_compare_exchange_n(&b, &b, 2, 1,  __ATOMIC_RELAXED,  __ATOMIC_RELAXED);
	__atomic_compare_exchange_n(&c, &c, 2, 1,  __ATOMIC_RELAXED,  __ATOMIC_RELAXED);
	__atomic_compare_exchange_n(&d, &d, 2, 1,  __ATOMIC_RELAXED,  __ATOMIC_RELAXED);

	return 0;
}

And looked at which symbols were unresolved. For the __atomic_*()
ones, we tested with and without -latomic to see which variants are
built-in, which variants require libatomic. This testing effort has
led to the following results:

                __sync       __atomic    gcc
               1  2  4  8    1  2  4  8
ARC            Y  Y  Y  -    Y  Y  Y  L   4.8 [with BR2_ARC_ATOMIC_EXT]
ARC            -  -  -  -    L  L  L  L   4.8 [without BR2_ARC_ATOMIC_EXT]
ARM            Y  Y  Y  X    Y  Y  Y  Y   4.8, 4.7
ARM            Y  Y  Y  -                 4.5
AArch64        Y  Y  Y  Y    Y  Y  Y  Y   4.9, 5.1
Bfin           -  -  Y  -                 4.3
i386 (i386)    -  -  -  -    L  L  L  L   4.9
i386 (i486..)  Y  Y  Y  -    L  L  L  L   4.9 [i486, c3, winchip2, winchip-c6]
i386 (> i586)  Y  Y  Y  Y    L  L  L  L   4.9
Microblaze     -  -  Y  -    L  L  Y  L   4.9
MIPS           Y  Y  Y  -    Y  Y  Y  L   4.9
MIPS64         Y  Y  Y  Y    Y  Y  Y  Y   4.9
NIOS 2         Y  Y  Y  -    Y  Y  Y  L   4.9, 5.2
PowerPC        Y  Y  Y  -    Y  Y  Y  L   4.9
SuperH         Y  Y  Y  -    Y  Y  Y  L   4.9
SPARC          -  -  -  -    L  L  L  L   4.9
SPARC64        Y  Y  Y  Y    Y  Y  Y  Y   4.9
x86_64         Y  Y  Y  Y    Y  Y  Y  Y   4.7, 4.9
Xtensa         Y  Y  Y  -    Y  Y  Y  Y   4.9

Notes:

 * __atomic built-ins appeared in gcc 4.7, so for toolchais older than
   that, the __atomic column is empty.

 * Y means 'supported built-in'

 * L means 'supported via linking to libatomic' (only for __atomic
   functions)

 * X indicates a very special case for 8 bytes __sync built-ins on
   ARM. On ARMv7, there is no problem, starting from gcc 4.7, the
   __sync built-in for 8 bytes integers is implemented, fully in
   userspace. For cores < ARMv7, doing a 8 bytes atomic operation
   requires help from the kernel. Unfortunately, the libgcc code
   implementing this uses the __write() function to display an error,
   and this function is internal to glibc. Therefore, if you're using
   glibc everything is fine, but if you're using uClibc or musl, you
   cannot link an application that uses 8 bytes __sync
   operations. This has been fixed as part of gcc PR68095, merged in
   the gcc 5 branch but not yet part of any gcc release.

 * - means not supported

This commit only introduces the new options. Follow-up commits will
progressively change the packages using BR2_ARCH_HAS_ATOMICS to use
the appropriate BR2_TOOLCHAIN_HAS_SYNC_x or BR2_TOOLCHAIN_HAS_ATOMIC
until the point where BR2_ARCH_HAS_ATOMICS can be removed.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
2016-02-06 11:16:00 +01:00

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# Generic toolchain options
# we want gdb config in the middle of both source and external
# toolchains, but mconf won't let us source the same file twice,
# so put it here instead
source "package/gdb/Config.in.host"
config BR2_TOOLCHAIN_HAS_NATIVE_RPC
bool
config BR2_USE_WCHAR
bool
config BR2_ENABLE_LOCALE
bool
config BR2_INSTALL_LIBSTDCPP
bool
config BR2_TOOLCHAIN_HAS_THREADS
bool
config BR2_TOOLCHAIN_HAS_THREADS_DEBUG
bool
config BR2_TOOLCHAIN_HAS_THREADS_NPTL
bool
config BR2_TOOLCHAIN_HAS_SHADOW_PASSWORDS
bool
config BR2_TOOLCHAIN_HAS_SSP
bool
config BR2_ENABLE_LOCALE_PURGE
bool "Purge unwanted locales"
help
Explicitly specify what locales to install on target. If N
then all locales supported by packages are installed.
config BR2_ENABLE_LOCALE_WHITELIST
string "Locales to keep"
default "C en_US de fr"
depends on BR2_ENABLE_LOCALE_PURGE
help
Whitespace seperated list of locales to allow on target.
Locales not listed here will be removed from the target.
See 'locale -a' on your host for a list of locales available
on your build host, or have a look in /usr/share/locale in
the target file system for available locales.
Notice that listing a locale here doesn't guarantee that it
will be available on the target - That purely depends on the
support for that locale in the selected packages.
config BR2_GENERATE_LOCALE
string "Generate locale data"
default ""
depends on \
(BR2_TOOLCHAIN_BUILDROOT_UCLIBC && BR2_ENABLE_LOCALE) || \
BR2_TOOLCHAIN_USES_GLIBC
help
Generate support for a list of locales. Locales can be
specified with or without encoding, when no encoding is
specified, UTF-8 is assumed. Examples of locales: en_US,
fr_FR.UTF-8.
config BR2_TOOLCHAIN_GLIBC_GCONV_LIBS_COPY
bool "Copy gconv libraries"
depends on BR2_TOOLCHAIN_USES_GLIBC
help
The gconv libraries are used to convert between different
character sets (charsets).
Say 'y' if you need to store and/or display different charsets.
config BR2_TOOLCHAIN_GLIBC_GCONV_LIBS_LIST
string "Gconv libraries to copy"
depends on BR2_TOOLCHAIN_GLIBC_GCONV_LIBS_COPY
help
Set to the list of gconv libraries to copy.
Leave empty to copy all gconv libraries.
Specify only the basename of the libraries, leave
out the .so extension. Eg.:
IBM850 ISO8859-15 UNICODE
Note: the full set of gconv libs are ~8MiB (on ARM).
# glibc and eglibc directly include gettext, so a separatly compiled
# gettext isn't needed and shouldn't be built to avoid conflicts. Some
# packages always need gettext, other packages only need gettext when
# locale support is enabled. See the documentation for how packages
# should rely on the following two options.
config BR2_NEEDS_GETTEXT
bool
default y if BR2_TOOLCHAIN_USES_UCLIBC
config BR2_NEEDS_GETTEXT_IF_LOCALE
bool
default y if (BR2_NEEDS_GETTEXT && BR2_ENABLE_LOCALE)
config BR2_USE_MMU
bool "Enable MMU support" if BR2_ARCH_HAS_MMU_OPTIONAL
default y if BR2_ARCH_HAS_MMU_OPTIONAL || BR2_ARCH_HAS_MMU_MANDATORY
help
If your target has a MMU, you should say Y here. If you
are unsure, just say Y.
config BR2_TARGET_OPTIMIZATION
string "Target Optimizations"
default ""
help
Optimizations to use when building for the target host.
NOTE: gcc optimization level is defined in build options.
config BR2_TARGET_LDFLAGS
string "Target linker options"
help
Extra options to pass to the linker when building for the target.
Note that options with a '$' sign (eg. -Wl,-rpath='$ORIGIN/../lib')
are not supported.
config BR2_ECLIPSE_REGISTER
bool "Register toolchain within Eclipse Buildroot plug-in"
help
This options tells Buildroot to generate the necessary
configuration files to make your toolchain appear within
Eclipse, through the Eclipse Buildroot plugin.
# Options for packages to depend on, if they require at least a
# specific version of the kernel headers.
# Toolchains should choose the adequate option (ie. the highest
# version, not all of them).
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0
bool
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_1
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_2
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_1
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_3
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_2
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_4
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_3
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_5
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_4
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_6
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_5
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_7
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_6
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_8
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_7
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_9
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_8
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_10
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_9
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_11
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_10
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_12
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_11
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_13
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_12
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_14
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_13
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_15
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_14
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_16
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_15
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_17
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_16
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_18
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_17
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_19
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_18
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_0
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_19
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_1
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_0
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_2
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_1
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_3
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_2
config BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_4
bool
select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_3
# This order guarantees that the highest version is set, as kconfig
# stops affecting a value on the first matching default.
config BR2_TOOLCHAIN_HEADERS_AT_LEAST
string
default "4.4" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_4
default "4.3" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_3
default "4.2" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_2
default "4.1" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_1
default "4.0" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_0
default "3.19" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_19
default "3.18" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_18
default "3.17" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_17
default "3.16" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_16
default "3.15" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_15
default "3.14" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_14
default "3.13" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_13
default "3.12" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_12
default "3.11" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_11
default "3.10" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_10
default "3.9" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_9
default "3.8" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_8
default "3.7" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_7
default "3.6" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_6
default "3.5" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_5
default "3.4" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_4
default "3.3" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_3
default "3.2" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_2
default "3.1" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_1
default "3.0" if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0
default "2.6"
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_3
bool
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_4
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_3
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_5
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_4
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_6
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_5
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_7
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_6
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_7
config BR2_TOOLCHAIN_GCC_AT_LEAST_4_9
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
config BR2_TOOLCHAIN_GCC_AT_LEAST_5
bool
select BR2_TOOLCHAIN_GCC_AT_LEAST_4_9
# This order guarantees that the highest version is set, as kconfig
# stops affecting a value on the first matching default.
config BR2_TOOLCHAIN_GCC_AT_LEAST
string
default "5" if BR2_TOOLCHAIN_GCC_AT_LEAST_5
default "4.9" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_9
default "4.8" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
default "4.7" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_7
default "4.6" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_6
default "4.5" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_5
default "4.4" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_4
default "4.3" if BR2_TOOLCHAIN_GCC_AT_LEAST_4_3
config BR2_TOOLCHAIN_HAS_SYNC_1
bool
default y
depends on !BR2_x86_i386
depends on !BR2_bfin
depends on !BR2_microblaze
depends on !BR2_sparc
depends on !(BR2_arc && !BR2_ARC_ATOMIC_EXT)
config BR2_TOOLCHAIN_HAS_SYNC_2
bool
default y if BR2_TOOLCHAIN_HAS_SYNC_1
config BR2_TOOLCHAIN_HAS_SYNC_4
bool
default y
depends on !BR2_sparc
depends on !BR2_x86_i386
depends on !(BR2_arc && !BR2_ARC_ATOMIC_EXT)
# The availability of __sync for 8-byte types on ARM is somewhat
# complicated:
#
# - It appeared in gcc starting with gcc 4.7.
#
# - On ARMv7, there is no problem, it can be directly implemented in
# userspace.
#
# - On < ARMv7, it requires help from the kernel. Unfortunately, the
# libgcc code implementing 8-byte __sync with the help from the
# kernel calls __write() when a failure occurs, which is a function
# internal to glibc, not available in uClibc and musl. This means
# that the 8-byte __sync operations are not available on < ARMv7
# with uClibc and musl. This problem was fixed as part of gcc
# PR68059, which was backported to the gcc 5 branch, but isn't yet
# part of any gcc 5.x release.
#
config BR2_TOOLCHAIN_ARM_HAS_SYNC_8
bool
default y
depends on BR2_arm || BR2_armeb
depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_7
depends on BR2_TOOLCHAIN_USES_GLIBC || BR2_ARM_CPU_ARMV7A
# 8-byte intrinsics available on most x86 CPUs, except a few old ones
config BR2_TOOLCHAIN_X86_HAS_SYNC_8
bool
default y
depends on BR2_i386
depends on !BR2_x86_i386
depends on !BR2_x86_i486
depends on !BR2_x86_c3
depends on !BR2_x86_winchip_c6
depends on !BR2_x86_winchip2
# 8-byte intrinsics available:
# - On all 64 bits architecture
# - On a certain combinations of ARM platforms
# - On certain x86 32 bits CPUs
config BR2_TOOLCHAIN_HAS_SYNC_8
bool
default y if BR2_ARCH_IS_64
default y if BR2_TOOLCHAIN_ARM_HAS_SYNC_8
default y if BR2_TOOLCHAIN_X86_HAS_SYNC_8
# __atomic intrinsics are available:
# - with gcc 4.8, either through built-ins or libatomic, on all
# architectures
# - with gcc 4.7, libatomic did not exist, so only built-ins are
# available. This means that __atomic can only be used in a subset
# of the architectures
config BR2_TOOLCHAIN_HAS_ATOMIC
bool
default y if BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
default y if BR2_TOOLCHAIN_GCC_AT_LEAST_4_7 && BR2_arm
default y if BR2_TOOLCHAIN_GCC_AT_LEAST_4_7 && BR2_armeb
default y if BR2_TOOLCHAIN_GCC_AT_LEAST_4_7 && BR2_xtensa
default y if BR2_TOOLCHAIN_GCC_AT_LEAST_4_7 && BR2_ARCH_IS_64
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